In the coating of electric appliance, office appliance and the like, powder coating has been widely used. In these areas, coating stain by magic ink and tobacco smoke has often caused serious troubles and there are always big demands to have a powder coating being excellent in stain resistance.
In Japanese Patent Publication (unexamined) No. 16778/90, as a measure for improving stain resistance, there discloses a powder coating comprising a hydroxyl group containing polyester resin and blocked isocyanate hardener, added with an acrylic resin containing a particular amount of hydroxyl group and glycidyl group. This technique is, however, only effective for the powder coating based on hydroxyl containing polyester and blocked isocyanate hardener and no improvement in stain resistance can be expected with other type of powder coating.
In Japanese Patent Publication (unexamined) No. 178361/90, there discloses a technique wherein particular acrylic resin microparticles defined by glass transition temperature and SP vale and having an average diameter of 0.001 to 10 microns are existed on the surfaces of the respective powder coating particles, thereby improving stain resistance of the formed coating. In this method, a high molecular weight acrylic resin is always locatized on the surface of the applied coating and therefore, this technique is very useful for all of polyester, epoxy- and acryl- powder coatings and however, in the preparation of powder coating, there needs an additional step of combining acrylic resin microparticles with the mother powder coating, which always push-up manufacturing cost of the powder coating.
It is, therefore, an object of the invention to provide a powder coating which is excellent in stain resistance, can be easily and economically obtained by following a conventional way, without changing any steps involved, and by using any combinations of base resin and hardener heretofore proposed.